Achievements in Stereoscopic Digital Cinema have brought some new challenges in the reproduction of scene objects that appear to be closer to the theatre audience, i.e. to be front image-plane objects. If these elements happen to move dynamically, they may be displayed, or projected on the screen, with some motion jumpiness (also called judder). Alternatively, if the same objects, presenting themselves closer to the viewer, move with speed below a certain nominal value, their naturally captured motion blur will be visualized with more pronounced effect. Classical film cinema and 2D Digital Cinema are not affected by the above correlation between the motion blur amount and the image depth. However, this correlation has a variable behavior in 3D imaging. With this phenomenon there emerges a new problem, pertaining to the Stereoscopic Three-Dimensional (S3D) depth portrayal. It has a slightly irritating effect on the audience, caused by the discrepancy of the correlation between motion blur and image depth, which adds to the discomfort of wearing special glasses during 3D presentations.
There is little published work regarding the irregular motion particularities of dynamic scene objects which appear in the front viewing plane of a stereoscopic cinema projection. And yet, the present method uses some image processing techniques that are known in the existing practice at the cinema theatres. It employs differently the motion blur fundamentals for the purpose of stereoscopic imagery.
There are two categories of methods aimed at improving motion reproduction, to which the present invention could be compared:
The first category includes methods for adding motion blur to reduce the frames per second rate in stereoscopic 3D digital cinema. These methods aim to reduce the frame repetition rate from 72 FPS to 48 FPS, per eye, by enhancing the directional inter-frame scene object trails. The motion blur field is extracted for each eye-image during the post-production phase of the movie mastering. The added picture components are tiny, but they contribute to the elimination of the motion breaking effect, associated with high-speed objects in the sequence of left eye (LE)-right eye (RE) frames, when the frame repetition is at the standard value of 48 FPS. The advantage of this category of methods is the rendering of the stereoscopic imagery to add adaptive motion blur and thus reduce the judder artifacts. The disadvantage of these methods is that their motion analysis is based only on the classic inter-frame difference, which does not encompass the particularities of the 3D pictures.
The second category includes methods for limiting the proximity (closeness) of 3D scene objects to the viewers. This approach restricts the value of the convergence offset range, e.g. it limits the extent to which the viewers in the theatre will have to cross their eyes so they can perceive the stereoscopic pictures as a 3D phenomenon. The initial convergence is determined during the camera acquisition and can be modified to some extent during post-production. By limiting the proximity (or rather the appearance of closeness) to the viewers, the motion artifact is also reduced, since the closer the objects are in the virtual space between the projection screen and the audience, the more artifacts are visible. The advantage of this category of methods is in their relative simplicity in achieving improved motion reproduction: That is achieved by convergence correction, which is a parallel image shift process. Their disadvantage is that these methods affect the creative decision of the movie authors and directors by manipulating the convergence and thus the stereoscopic intention of the presentation.
Another consequence of the function of the motion blur amount is electronic convergence. As one of the eye-images shifts horizontally relative to the other eye-image, the scene objects could appear closer to the viewer. Since the human brain concentrates better on the closer zone, the acuity of the Human Visual System (HVS) highlights any motion disproportion. To counteract this problem, what is needed is a method and apparatus to recognize and optimize the relation between motion blur and the changed (modified, corrected) electronic convergence. The term electronic convergence here defines the shifting between LE and RE image in video domain, done at post-production.